The present invention relates to defoaming methods and compositions and, more particularly, to methods and compositions for hindering the formation of foam or breaking foam in well treatment fluids.
Defoaming compositions have long been used in the oil and gas industry and other industries to hinder the formation of foam, hinder entrainment of a gas in a liquid, or break previously formed foam. For example, defoaming compositions are commonly utilized as components in liquids used in subterranean operation, such as well treatment fluids to hinder the formation of foam or the entrainment of a gas in the liquids during the preparation and/or pumping of the fluid. Also, defoaming compositions have traditionally been utilized for breaking previously foamed treatment fluids. For example, when a foamed well treatment fluid must be disposed of on the surface, a defoaming composition may be added to the fluid to destroy the foam, thus, facilitating disposal of the liquid components of the treating fluid.
Defoaming compositions and methods may be employed to avoid adverse consequences associated with inadvertent formation of foam or entrainment of gas in well treatment fluids, such as drilling fluids, stimulation fluids, cement compositions, and completion fluids. For example, if well treatment fluids are inadvertently foamed or air is entrained into the fluids while being agitated, mixed and/or pumped, an associated change in density of the well treatment fluid may interfere with the operation of pumps (e.g., positive displacement pumps) designed to move the well treatment fluid. In another example, foaming and entrained gas may impact the desired operation of the well treatment fluid by changing the characteristics (e.g., density or viscosity) of the well treatment fluid. For example, if a well cement composition is foamed or otherwise entrains air during pumping and/or mixing, the density of the resulting cement composition may be considerably lower than the desired or required density. This reduction in the density of the cement composition may prevent the cement composition from exerting a desired hydrostatic pressure on a formation, prevent the cement composition from having sufficient compressive strength, and so forth.
A variety of defoaming compositions have traditionally been utilized in the oil and gas industry. Examples of such defoaming compositions utilized in well treatment fluids include compositions of glycerol tristerate and one or more aliphatic hydrocarbons. Other defoaming compositions that have been utilized include propylene glycol and a mixture of propylene glycol with a copolymer of ethylene oxide and propylene oxide monomers. While these defoaming compositions may function adequately to prevent the formation of foam in well treatment fluids when they are prepared and pumped, they may not function adequately for defoaming previously foamed well treatment fluids, and particularly previously foamed well cement compositions. Still other defoaming compositions include mixtures of polypropylene glycol, particulate hydrophobic silica, and a liquid diluent. While these defoaming compositions may function adequately to prevent or reduce foaming after initial preparation, it is now recognized that the silica in these compositions settles within about 6 months, which may cause problems with consistency and pouring of such defoaming compositions from storage containers. This may effectively reduce the shelf life of these defoaming compositions to less than 9 months.